Substrate processing apparatus, substrate processing method, and recording medium

ABSTRACT

A substrate processing apparatus performs: a pressure raising process of raising a pressure within the processing container to a processing pressure higher than a critical pressure of the processing fluid, after the substrate is accommodated in the processing container; and a circulation process of supplying the processing fluid to the processing container and discharging the processing fluid from the processing container while keeping a pressure at which the processing fluid is maintained in the supercritical state, within the processing container. In the pressure raising process, the supply of the processing fluid from the second fluid supply unit is stopped and the processing fluid is supplied from the first fluid supply unit into the processing container until at least the pressure within the processing container reaches the critical pressure. In the circulation process, the processing fluid is supplied into the processing container from the second fluid supply unit.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based on and claims priority from Japanese PatentApplication No. 2016-216313, filed on Nov. 4, 2016, with the JapanPatent Office, the disclosure of which is incorporated herein in itsentirety by reference.

TECHNICAL FIELD

The present disclosure relates to a technique of drying aliquid-adhering substrate using a processing fluid in a supercriticalstate.

BACKGROUND

In a semiconductor device manufacturing process where a stackedstructure of an integrated circuit is formed on the surface of asubstrate such as, for example, a semiconductor wafer (hereinafter,referred to as a “wafer”), a liquid processing such as, for example, achemical liquid cleaning or a wet etching is performed. In order toremove, for example, a liquid adhering to the surface of the wafer dueto such a liquid processing, a drying method using a processing fluid ina supercritical state has recently been used (see e.g., Japanese PatentLaid-Open Publication No. 2013-012538).

In the drying method, in the case where a fine pattern with a highaspect ratio is formed on the surface of the substrate, when a liquidwithin a recess of the pattern evaporates before the liquid within therecess of the pattern is replaced with the processing fluid in thesupercritical state, a pattern collapse occurs. It is required toestablish a technique of more reliably avoiding the occurrence of suchan event.

SUMMARY

According to an aspect of the present disclosure, there is provided asubstrate processing apparatus for drying a substrate having a liquidadhering to a surface thereof, using a processing fluid in asupercritical state. The substrate processing apparatus includes: aprocessing container; a substrate holder configured to horizontally holdthe substrate within the processing container in a state in which thesurface of the substrate is directed upwards; a first fluid supply unitprovided below the substrate held by the substrate holder, andconfigured to supply a pressurized processing fluid; a second fluidsupply unit provided at a side of the substrate held by the substrateholder, and configured to supply a pressurized processing fluid; a fluiddischarge unit configured to discharge a processing fluid from theprocessing container; and a controller configured to control operationsof the first fluid supply unit, the second fluid supply unit, and thefluid discharge unit. The controller causes the substrate processingapparatus to execute: a pressure raising process of supplying thepressurized processing fluid to the processing container so as to raisea pressure within the processing container to a processing pressurehigher than a critical pressure of the processing fluid, after thesubstrate having the liquid adhering to the surface thereof isaccommodated in the processing container; and a circulation process ofsupplying the processing fluid to the processing container anddischarging the processing fluid from the processing container whilekeeping a pressure at which at least the processing fluid is maintainedin the supercritical state, within the processing container. In thepressure raising process, the controller causes a supply of theprocessing fluid from the second fluid supply unit to be stopped and theprocessing fluid to be supplied from the first fluid supply unit intothe processing container until at least the pressure within theprocessing container reaches the critical pressure of the processingfluid, and in the circulation process, the controller causes theprocessing fluid to be supplied into the processing container from thesecond fluid supply unit.

The foregoing summary is illustrative only and is not intended to be inany way limiting. In addition to the illustrative aspects, embodiments,and features described above, further aspects, embodiments, and featureswill become apparent by reference to the drawings and the followingdetailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional plan view illustrating the overallconfiguration of a substrate processing system.

FIG. 2 is an external perspective view of a processing container of asupercritical processing device.

FIG. 3 is a sectional view of the processing container.

FIG. 4 is a piping system view of the supercritical processing device.

FIGS. 5A to 5D are views for explaining a drying mechanism of IPA.

FIG. 6 is a graph illustrating a change of a pressure within theprocessing container during a drying process.

FIG. 7 is a graph illustrating a relationship between a CO₂concentration, and a critical temperature and a critical pressure, in amixed fluid containing IPA and CO₂.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawing, which form a part hereof. The illustrativeembodiments described in the detailed description, drawing, and claimsare not meant to be limiting. Other embodiments may be utilized, andother changes may be made without departing from the spirit or scope ofthe subject matter presented here.

An object of the present disclosure is to provide a technique ofpreventing a liquid within a recess of a pattern from evaporating beforebeing replaced with a processing fluid in a supercritical state.

According to an aspect of the present disclosure, there is providedsubstrate processing apparatus for drying a substrate having a liquidadhering to a surface thereof, using a processing fluid in asupercritical state. The substrate processing apparatus includes: aprocessing container; a substrate holder configured to horizontally holdthe substrate within the processing container in a state in which thesurface of the substrate is directed upwards; a first fluid supply unitprovided below the substrate held by the substrate holder, andconfigured to supply a pressurized processing fluid; a second fluidsupply unit provided at a side of the substrate held by the substrateholder, and configured to supply a pressurized processing fluid; a fluiddischarge unit configured to discharge a processing fluid from theprocessing container; and a controller configured to control operationsof the first fluid supply unit, the second fluid supply unit, and thefluid discharge unit. The controller causes the substrate processingapparatus to execute: a pressure raising process of supplying thepressurized processing fluid to the processing container so as to raisea pressure within the processing container to a processing pressurehigher than a critical pressure of the processing fluid, after thesubstrate having the liquid adhering to the surface thereof isaccommodated in the processing container; and a circulation process ofsupplying the processing fluid to the processing container anddischarging the processing fluid from the processing container whilekeeping a pressure at which at least the processing fluid is maintainedin the supercritical state, within the processing container. In thepressure raising process, the controller causes a supply of theprocessing fluid from the second fluid supply unit to be stopped and theprocessing fluid to be supplied from the first fluid supply unit intothe processing container until at least the pressure within theprocessing container reaches the critical pressure of the processingfluid, and in the circulation process, the controller causes theprocessing fluid to be supplied into the processing container from thesecond fluid supply unit.

In the above-described substrate processing apparatus, in the pressureraising process, the controller causes the supply of the processingfluid from the second fluid supply unit to be stopped and the processingfluid to be supplied from the first fluid supply unit into theprocessing container until the pressure within the processing containerreaches the processing pressure via the critical pressure from a pointin time when the supply of the processing fluid into the processingcontainer starts.

In the above-described substrate processing apparatus, in the pressureraising process, the controller causes the supply of the processingfluid from the second fluid supply unit to be stopped and the processingfluid to be supplied from the first fluid supply unit into theprocessing container until the pressure within the processing containerreaches the critical pressure of the processing fluid from a point intime when a supply of the processing fluid into the processing containerstarts, and the controller causes the supply of the processing fluidfrom the first fluid supply unit to be stopped and the processing fluidto be supplied from the second fluid supply unit into the processingcontainer, or the processing fluid to be supplied from both the firstand second fluid supply units into the processing container, until thepressure within the processing container reaches the processing pressureafter reaching the critical pressure of the processing fluid.

In the above-described substrate processing apparatus, the first fluidsupply unit is provided to supply the processing fluid from a positionbelow a central portion of the substrate held by the substrate holder,toward the central portion of the substrate.

In the above-described substrate processing apparatus, the second fluidsupply unit is provided to supply the processing fluid from a side ofthe substrate substantially in a horizontal direction.

In the above-described substrate processing apparatus, the second fluidsupply unit is provided to supply the processing fluid in parallel tothe substrate from a position higher than an upper surface of thesubstrate, at the side of the substrate.

According to another aspect of the present disclosure, there is provideda substrate processing method that includes: accommodating a substratehaving a pattern formed on a surface thereof and a liquid adhering tothe surface, in a processing container; raising a pressure within theprocessing container to a processing pressure higher than a criticalpressure of the processing fluid by supplying a pressurized processingfluid to the processing container; and performing a circulation processof supplying the pressurized processing fluid to the processingcontainer and discharging the processing fluid from the processingcontainer while keeping a pressure at which at least the processingfluid is maintained in a supercritical state, within the processingcontainer. In the raising of the pressure, the pressurized processingfluid is supplied from a first fluid supply unit provided below thesubstrate until at least the pressure within the processing containerreaches the critical pressure of the processing fluid, in the performingof the circulation process, the pressurized processing fluid is suppliedfrom a second fluid supply unit provided at a side of the substrate, andin the raising of the pressure, the pressurized processing fluid is notsupplied from the second fluid supply unit until at least the pressurewithin the processing container reaches the critical pressure of theprocessing fluid.

In the above-described method, in the raising of the pressure, theprocessing fluid is supplied into the processing container using thefirst fluid supply unit without using the second fluid supply unit untilthe pressure within the processing container reaches the processingpressure via the critical pressure from a point in time when the supplyof the processing fluid into the processing container starts.

In the above-described method, in the raising of the pressure, theprocessing fluid is supplied into the processing container using thefirst fluid supply unit without using the second fluid supply unit untilthe pressure within the processing container reaches the criticalpressure of the processing fluid from a point in time when a supply ofthe processing fluid into the processing container starts, and theprocessing fluid is supplied into the processing container using thesecond fluid supply unit without using the first fluid supply unit orthe processing fluid is supplied into the processing container usingboth the first and second fluid supply units until the pressure withinthe processing container reaches the processing pressure after reachingthe critical pressure of the processing fluid.

According to yet another aspect of the present disclosure, there isprovided non-transitory computer-readable storage medium storing acomputer-executable program that, when executed, causes a computer tocontrol a substrate processing apparatus to execute the substrateprocessing method described above.

According to the exemplary embodiment of the present disclosure, it ispossible to prevent a liquid within a recess of a pattern fromevaporating before being replaced with a processing fluid in asupercritical state.

Hereinafter, an exemplary embodiment of the present disclosure will bedescribed with reference to drawings. Meanwhile, the configurationillustrated in the drawings attached to the present specification mayinclude portions in which, for example, sizes and scales are changedfrom those of actual ones for convenience of illustration and ease ofunderstanding.

[Configuration of Substrate Processing System]

As illustrated in FIG. 1, a substrate processing system 1 includes: aplurality of cleaning devices 2 (two cleaning devices 2 in the exampleillustrated in FIG. 1) configured to perform a cleaning process bysupplying a cleaning liquid to a wafer W; and a plurality ofsupercritical processing devices 3 (six supercritical processing devices3 in the example illustrated in FIG. 1) configured to remove adry-preventing liquid (isopropyl alcohol (IPA) in the present exemplaryembodiment) adhering to the wafer W after the cleaning process bybringing the dry-preventing liquid into contact with a processing fluidin a supercritical state (carbon dioxide (CO₂) in the present exemplaryembodiment).

In the substrate processing system 1, a FOUP 100 is placed in a placingsection 11, and wafers W stored in the FOUP 100 are transferred to acleaning processing section 14 and a supercritical processing section 15via a carry-in/out section 12 and a transfer section 13. In the cleaningprocessing section 14 and the supercritical processing section 15,first, the wafers W are carried into the cleaning device 2 provided inthe cleaning processing section 14 and subjected to a cleaning process.Then, the wafers W are carried into the supercritical processing device3 provided in the supercritical processing section 15, and subjected toa drying process in which IPA is removed from the wafers W. In FIG. 1, areference numeral “121” indicates a first conveyance mechanismconfigured to convey wafers W between the FOUP 100 and the transfersection 13, and a reference numeral “131” indicates a delivery shelfserving as a buffer in which the wafers W being conveyed between thecarry-in/out section 12, and the cleaning processing section 14 and thesupercritical processing section 15 are temporarily placed.

A wafer conveyance path 162 is connected to an opening of the transfersection 13, and the cleaning processing section 14 and the supercriticalprocessing section 15 are provided along the wafer conveyance path 162.In the cleaning processing section 14, a total of two cleaning devices 2are provided, that is, one cleaning device 2 at one side and onecleaning device 2 at the other side are disposed across the waferconveyance path 162. Meanwhile, in the supercritical processing section15, a total of six supercritical processing devices 3 functioning assubstrate processing apparatuses configured to perform a drying processof removing IPA from wafers W are provided, that is, three supercriticalprocessing devices 3 at one side and three supercritical processingdevices 3 at the other side are disposed across the wafer conveyancepath 162. A second conveyance mechanism 161 is disposed in the waferconveyance path 162, and the second conveyance mechanism 161 is providedto be movable within the wafer conveyance path 162. The wafer W placedon the delivery shelf 131 is received by the second conveyance mechanism161, and the second conveyance mechanism 161 carries the wafers W intothe cleaning device 2 and the supercritical processing device 3.Meanwhile, the number and the arrangement mode of the cleaning devices 2and the supercritical processing devices 3 are not particularly limited,but an appropriate number of cleaning devices 2 and an appropriatenumber of supercritical processing devices 3 are disposed in anappropriate mode according to, for example, the number of wafers Wprocessed per unit time and a processing time of each cleaning device 2and each supercritical processing device 3.

The cleaning device 2 is configured as, for example, a single wafer-typedevice that cleans the wafers W one by one by spin cleaning. In thiscase, while each wafer W is horizontally held and rotated around avertical axis, a chemical liquid for cleaning or a rinse liquid forwashing off the chemical liquid are supplied to a processing surface ofthe wafer W at an appropriate timing so that a cleaning process of thewafer W may be performed. The chemical liquid and the rinse liquid usedin the cleaning device 2 are not particularly limited. For example, anSC1 liquid (that is, a mixed liquid of ammonia and hydrogen peroxide)which is an alkaline chemical liquid may be supplied to the wafer W toremove particles or organic pollutants from the wafer W. Then, deionizedwater (DIW) that is a rinse liquid may be supplied to the wafer W towash off the SC1 liquid from the wafer W. A dilute hydrofluoric acidaqueous solution (diluted hydrofluoric acid (DHF)) which is an acidicchemical liquid may be supplied to the wafer W to remove a natural oxidefilm, and then DIW may be supplied to the wafer W to wash off the DHFaqueous solution from the wafer W.

Then, after a rinse process by the DIW is completed, the cleaning device2 supplies IPA as a dry-preventing liquid to the wafer W while rotatingthe wafer W, so that the DIW remaining on the processing surface of thewafer W is replaced with the IPA. Then, the rotation of the wafer W isgently stopped. Here, a sufficient amount of IPA is supplied to thewafer W, and a puddle of the IPA is formed on the surface of the wafer Wformed with a semiconductor pattern so that a liquid film of the IPA isformed on the surface of the wafer W. The wafer W keeping the puddle ofthe IPA is carried out of the cleaning device 2 by the second conveyancemechanism 161.

The IPA applied to the surface of the wafer W as described above servesto prevent the wafer W from being dried. Particularly, in order tosuppress the occurrence of a so-called pattern collapse on the wafer Wdue to IPA evaporation during the conveyance of the wafer W from thecleaning device 2 to the supercritical processing device 3, the cleaningdevice 2 applies a sufficient amount of IPA to the wafer W so that anIPA film with a relatively large thickness may be formed on the surfaceof the wafer W.

The wafer W carried out of the cleaning device 2 is carried into aprocessing container of the supercritical processing device 3 by thesecond conveyance mechanism 161 in the state in which the IPA is spreadthereon. Then, a drying process of the IPA is performed in thesupercritical processing device 3.

[Supercritical Processing Device]

Hereinafter, descriptions will be made of the supercritical processingdevice 3 with reference to FIGS. 2 to 4.

As illustrated in FIGS. 2 and 3, a processing container 301 includes acontainer main body 311 in which an opening 312 through which a wafer Wis loaded and unloaded is formed, a holding plate 316 that horizontallyholds the wafer W as a processing target, and a lid member 315 thatsupports the holding plate 316, and air-tightly seals the opening 312when the wafer W is carried into the container main body 311.

The container main body 311 is a container inside which a processingspace capable of accommodating, for example, a wafer W with a diameterof 300 mm is formed. A fluid supply header (a first fluid supply unit)317 is provided at one end side within the container main body 311, anda fluid discharge header (a fluid discharge unit) 318 is provided at theother end side. In the illustrated example, the fluid supply header 317is constituted by a block body in which a large number of openings(first fluid supply ports) are formed, and the fluid discharge header318 is constituted by a pipe in which a large number of openings (fluiddischarge ports) are formed. The first fluid supply ports of the fluidsupply header 317 may be located at a position slightly higher than theupper surface of the wafer W held by the holding plate 316.

The configuration of the fluid supply header 317 and the fluid dischargeheader 318 is not limited to the illustrated example, but, for example,the fluid discharge header 318 may be formed as a block body, and thefluid supply header 317 may be formed as a pipe.

When the holding plate 316 is viewed from below, the holding plate 316covers almost the entire area of the lower surface of the wafer W. Theholding plate 316 has an opening 316 a at an end portion at the lidmember 315 side. A processing fluid present in the space above theholding plate 316 is guided to the fluid discharge header 318 throughthe opening 316 a (see the arrow F5 in FIG. 3).

The fluid supply header 317 supplies the processing fluid into thecontainer main body 311 (the processing container 301) toward asubstantially horizontal direction. The horizontal direction mentionedherein refers to a direction perpendicular to a vertical direction inwhich a gravity acts, and generally to a direction parallel to adirection in which the flat surface of the wafer W held by the holdingplate 316 extends.

The fluid within the processing container 301 is discharged to theoutside of the processing container 301 through the fluid dischargeheader 318. The fluid discharged through the fluid discharge header 318includes not only the processing fluid supplied into the processingcontainer 301 through the fluid supply header 317, but also IPA adheringto the surface of the wafer W and dissolved in the processing fluid.

A fluid supply nozzle (a second fluid supply unit) 341 is provided atthe bottom portion of the container main body 311 to supply theprocessing fluid into the processing container 301. In the illustratedexample, the fluid supply nozzle 341 is configured with an openingformed in the bottom wall of the container main body 311. The fluidsupply nozzle 341 is located below (for example, just below) the centralportion of the wafer W, and supplies the processing fluid into theprocessing container 301 toward the central portion of the wafer W (forexample, vertically upwards).

The processing container 301 further includes a pressing mechanism (notillustrated). The pressing mechanism serves to press the lid member 315toward the container main body 311 against the internal pressure causedby the supercritical-state processing fluid supplied into the processingspace, thereby air-tightly sealing the processing space. It is desirableto provide, for example, an insulating material or a tape heater (notillustrated) at the ceiling wall or the bottom wall of the containermain body 311 such that the processing fluid supplied into theprocessing space is kept at a temperature of a supercritical state.

As illustrated in FIG. 4, the supercritical processing device 3 includesa fluid supply tank 51 which is a supply source of a processing fluid ina supercritical state, for example, a processing fluid at a highpressure ranging from about 16 MPa to 20 MPa (megapascals). A mainsupply line 50 is connected to the fluid supply tank 51. The main supplyline 50, in the middle thereof, diverges into a first supply line 63connected to the fluid supply header (the first fluid supply unit) 317within the processing container 301, and a second supply line 64connected to the fluid supply nozzle (the second fluid supply unit) 341.

An open/close valve 52 a, an orifice 55 a, a filter 57, and anopen/close valve 52 b are provided in order from the upstream sidebetween the fluid supply tank 51 and the fluid supply header 317 (thatis, the main supply line 50 and the first supply line 63 lead from themain supply line 50). The second supply line 64 diverges from the mainsupply line 50, at a location between the filter 57 and the open/closevalve 52 b. An open/close valve 52 c is provided in the second supplyline 64.

The orifice 55 a is provided to lower the flow velocity of theprocessing fluid supplied from the fluid supply tank 51 so as to protectthe wafer W. The filter 57 is provided to remove foreign matters(particle-causing substances) contained in the processing fluid flowingthrough the main supply line 50.

The supercritical processing device 3 further includes a purge gassupply line 70 connected to a purge device 62 through an open/closevalve 52 d and a check valve 58 a, and a discharge line 71 connected toa space outside the supercritical processing device 3 through anopen/close valve 52 e and an orifice 55 c. The purge gas supply line 70and the discharge line 71 are connected to the main supply line 50, thefirst supply line 63, and the second supply line 64.

The purge gas supply line 70 is used, for example, for the purpose offilling the processing container 301 with an inert gas, thereby keepinga clean state while the supply of the processing fluid from the fluidsupply tank 51 to the processing container 301 is stopped. The dischargeline 71 is used, for example, for discharging the processing fluidremaining within the supply line between the open/close valve 52 a andthe open/close valve 52 b to the outside while the supercriticalprocessing device 3 is powered OFF.

A main discharge line 65 is connected to the fluid discharge header 318within the processing container 301. The main discharge line 65, in themiddle thereof, branches into a first discharge line 66, a seconddischarge line 67, a third discharge line 68, and a fourth dischargeline 69.

An open/close valve 52 f, a back pressure valve 59, a concentrationsensor 60, and an open/close valve 52 g are provided in this order fromthe upstream side in the main discharge line 65 and the first dischargeline 66 lead from the main discharge line 65.

The back pressure valve 59 is opened when a primary side pressure (whichis the same as the pressure within the processing container 301) exceedsa set pressure, so that the fluid flows toward a secondary side and theprimary side pressure is kept at the set pressure. The set pressure ofthe back pressure valve 59 may be changed by the controller 4 at anytime.

The concentration sensor 60 is a sensor that measures an IPAconcentration in the fluid flowing through the main discharge line 65.

A needle valve (a variable throttle) 61 a and a check valve 58 b areprovided at the downstream side of the open/close valve 52 g in thefirst discharge line 66. The needle valve 61 a is a valve that adjusts aflow rate of the fluid discharged to the outside of the supercriticalprocessing device 3 through the first discharge line 66.

The second discharge line 67, the third discharge line 68, and thefourth discharge line 69 diverge from the main discharge line 65 at alocation between the concentration sensor 60 and the open/close valve 52g. An open/close valve 52 h, a needle valve 61 b, and a check valve 58 care provided in the second discharge line 67. An open/close valve 52 iand a check valve 58 d are provided in the third discharge line 68. Anopen/close valve 52 j and an orifice 55 d are provided in the fourthdischarge line 69.

The second discharge line 67 and the third discharge line 68 areconnected to a first discharge destination, for example, a fluidrecovery device, and the fourth discharge line 69 is connected to asecond discharge destination, for example, an atmospheric space outsidethe supercritical processing device 3 or a factory exhaust system.

When the fluid is discharged from the processing container 301, at leastone of the open/close valves 52 g, 52 h, 52 i, and 52 j is opened.Particularly, when the supercritical processing device 3 is stopped, theopen/close valve 52 j may be opened so that the fluid present in thefirst discharge line 66 between the concentration sensor 60 and theopen/close valve 52 g may be discharged to the outside of thesupercritical processing device 3.

A pressure sensor configured to detect the pressure of the fluid and atemperature sensor configured to detect the temperature of the fluid areprovided at various places of the line through which the fluid flows inthe supercritical processing device 3. In the example illustrated inFIG. 4, a pressure sensor 53 a and a temperature sensor Ma are providedbetween the open/close valve 52 a and the orifice 55 a, a pressuresensor 53 b and a temperature sensor 54 b are provided between theorifice 55 a and the filter 57, a pressure sensor 53 c. is providedbetween the filter 57 and the open/close valve 52 b, a temperaturesensor 54 c is provided between the open/close valve 52 b and theprocessing container 301, and a temperature sensor 54 d is providedbetween an orifice 55 b and the processing container 301. A pressuresensor 53 d and a temperature sensor 54 f are provided between theprocessing container 301 and the open/close valve 52 f, and a pressuresensor 53 e and a temperature sensor 54 g are provided between theconcentration sensor 60 and the open/close valve 52 g. A temperaturesensor 54 e is provided to detect the temperature of the fluid withinthe processing container 301.

Four heaters H are provided in the main supply line 50 and the firstsupply line 63 to adjust the temperature of the processing fluid to besupplied to the processing container 301. The heater H may also beprovided in the discharge line at the downstream side of the processingcontainer 301.

A safety valve (a relief valve) 56 a is provided between the orifice 55a and the filter 57 in the main supply line 50, a safety valve 56 b isprovided between the processing container 301 and the open/close valve52 f, and a safety valve 56 c is provided between the concentrationsensor 60 and the open/close valve 52 g. The safety valves 56 a to 56 curgently discharge the fluid within the line to the outside in the caseof an abnormality such as the case where the pressure within the line(the pipe) provided with the safety valves becomes excessive.

The controller 4 receives measurement signals from various sensors(e.g., the pressure sensors 53 a to 53 e, the temperature sensors 54 ato 54 g, and the concentration sensor 60) illustrated in FIG. 3, andsends control signals (e.g., open/close signals of the open/close valves52 a to 52 j, a set pressure regulating signal of the back pressurevalve 59, and opening degree regulating signals of the needle valves 61a and 61 b) to various functional elements. The controller 4 is, forexample, a computer, and includes a calculator 18 and a storage 19. Thestorage 19 stores a program that controls various processings to beexecuted in the substrate processing system 1. The calculator 18controls an operation of the substrate processing system 1 by readingand executing the program stored in the storage 19. The program may berecorded in a computer-readable storage medium, and then installed fromthe storage medium to the storage 19 of the controller 4. Thecomputer-readable storage medium may be, for example, a hard disk (HD),a flexible disk (FD), a compact disk (CD), a magneto-optical disk (MO),or a memory card.

[Supercritical Drying Process]

Hereinafter, brief descriptions will be made of a drying mechanism ofIPA using a processing fluid (for example, carbon dioxide (CO₂)) in asupercritical state, with reference to FIGS. 5A to 5D.

Immediately after a processing fluid R in a supercritical state isintroduced into the processing container 301, as illustrated in FIG. 5A,only IPA is present within a recess of a pattern P of a wafer W.

The IPA within the recess comes into contact with the processing fluid Rin the supercritical state, gradually dissolves in the processing fluidR, and is gradually replaced by the processing fluid R as illustrated inFIG. 5B. Here, in the recess, besides the IPA and the processing fluidR, a mixed fluid M in which the IPA is mixed with the processing fluid Ris present.

As the replacement of the IPA by the processing fluid R within therecess progresses, the IPA present within the recess decreases, andfinally, as illustrated in FIG. 5C, only the processing fluid R in thesupercritical state is present within the recess.

After the IPA is removed from the inside of the recess, the pressurewithin the processing container 301 is lowered to an atmosphericpressure. Thus, as illustrated in FIG. 5D, the processing fluid Rchanges from a supercritical state to a gas state, and the inside of therecess is occupied only by a gas. In this manner, the IPA within therecess of the pattern P is removed, and the drying process of the waferW is completed.

Next, descriptions will be made of a drying method (a substrateprocessing method) executed using the above described supercriticalprocessing device 3. Meanwhile, the drying method to be described belowis automatically executed based on a processing recipe and a controlprogram stored in the storage 19, under the control of the controller 4.

<Loading Process>

After having been subjected to a cleaning process in the cleaning device2, the wafer W is carried out of the cleaning device 2 by the secondconveyance mechanism 161 in a state where the inside of the recess ofthe pattern on the surface of the wafer W is filled with IPA and apuddle of the IPA is formed on the surface. The second conveyancemechanism 161 places the wafer on the holding plate 316, then theholding plate 316 on which the wafer is placed advances into thecontainer main body 311, and then the lid member 315 is engaged with thecontainer main body 311 in a sealing manner Accordingly, the loading ofthe wafer is completed.

Next, according to the order illustrated in the time chart of FIG. 6,the processing fluid (CO₂) is supplied into the processing container301, and a drying process of the wafer W is performed thereby. Polygonalline A illustrated in FIG. 6 indicates a relationship between an elapsedtime from a point in time when the drying process starts and a pressurewithin the processing container 301.

<Pressure Raising Process>

First, a pressure raising process (T1) is performed, and CO₂ (carbondioxide) as a processing fluid is supplied from the fluid supply tank 51into the processing container 301. Specifically, the open/close valves52 a, 52 c, and 52 f are opened, and the open/close valves 52 b and 52d, and the open/close valve 52 e are closed. The open/close valves 52 g,52 h, and 52 i are opened, and the open/close valve 52 j is closed. Theneedle valves 61 a and 61 b are adjusted to a predetermined openingdegree. The set pressure of the back pressure valve 59 is set to apressure at which CO₂ within the processing container 301 may be kept ata supercritical state, for example, 15 MPa. Accordingly, CO₂ in thesupercritical state at a pressure of about 16 MPa is ejected from thefluid supply tank 51, toward the lower surface of the holding plate 316through the fluid supply nozzle 341 just below the central portion ofthe wafer W.

CO₂ ejected from the fluid supply nozzle 341 (see arrow F1 in FIG. 3)collides with the holding plate 316 that covers the lower surface of thewafer W, radially spreads along the lower surface of the holding plate316 (see arrow F2 in FIG. 3), and then flows into the space at the uppersurface side of the wafer W through a gap between the edge of theholding plate 316 and the side wall of the container main body 311, andthe opening 316 a of the holding plate 316 (see the arrow F3 in FIG. 3).Since the back pressure valve 59 is kept fully closed until the setpressure (15 MPa) is reached, CO₂ does not flow from the processingcontainer 301. Thus, the pressure within the processing container 301gradually increases.

At the initial stage of the pressure raising process (T1), the pressureof CO₂ in the supercritical state fed from the fluid supply tank 51 islowered while CO₂ passes through the orifice 55 a, and also is loweredwhen CO₂ flows into the processing container 301 in a normal pressurestate. Accordingly, at the initial stage of the pressure raising process(T1), the pressure of CO₂ flowing into the processing container 301 islower than a critical pressure (for example, about 7 MPa), that is, CO₂in a gas state flows into the processing container 301. Then, as theinside of the processing container 301 is gradually filled with CO₂, thepressure within the processing container 301 gradually increases. Whenthe pressure within the processing container 301 exceeds a criticalpressure, CO₂ present within the processing container 301 is placed in asupercritical state.

In the pressure raising process (T1), when the pressure within theprocessing container 301 increases and exceeds the critical pressure,the processing fluid within the processing container 301 is placed inthe supercritical state, and IPA on the wafer W starts to dissolve inthe processing fluid in the supercritical state. Then, a mixing ratio ofIPA to CO₂ in a mixed fluid containing CO₂ and IPA gradually changes.Meanwhile, it cannot be said that the mixing ratio is uniform over theentire surface of the wafer W. In order to prevent an unexpectingpattern collapse by the vaporization of the mixed fluid, in the pressureraising process (T1), the pressure within the processing container 301rises to a pressure that ensures that CO₂ within the processingcontainer 301 is placed in a supercritical state (here, 15 MPa)regardless of the CO₂ concentration in the mixed fluid. Here, the“pressure that ensures that CO₂ is placed in the supercritical state” isa pressure higher than a maximum value of a pressure indicated by thecurve C in the graph of FIG. 7. The pressure (15 MPa) is called a“processing pressure.”

<Keeping Process>

When the pressure within the processing container 301 rises to theprocessing pressure (15 MPa) by the pressure raising process (T1), theopen/close valve 52 b and the open/close valve 52 f located at theupstream side and the downstream side of the processing container 301,respectively, are closed. Then, the process shifts to a keeping process(T2) in which the pressure within the processing container 301 is kept.The keeping process is continued until the IPA concentration and the CO₂concentration in the mixed fluid within the recess of the pattern P ofthe wafer W become predetermined concentrations (for example, IPAconcentration: 30% or less, CO₂ concentration: 70% or more). The timefor the keeping process (T2) may be determined through experiments. Inthe keeping process (T2), the open/close states of other valves are thesame as the open/close states in the pressure raising process (T1).

<Circulation Process>

A circulation process (T3) is performed after the keeping process (T2).The circulation process (T3) may be performed by alternately repeating apressure lowering step in which the mixed fluid of CO₂ and IPA isdischarged from the inside of the processing container 301 so as tolower the pressure within the processing container 301, and a pressureraising step in which new CO₂, which does not contain IPA, is suppliedinto the processing container 301 from the fluid supply tank 51 so as toraise the pressure within the processing container 301.

The circulation process (T3) is performed by opening, for example, theopen/close valve 52 b and the open/close valve 52 f, and repeatedlyraising and lowering the set pressure of the back pressure valve 59.Alternatively, the circulation process (T3) may be performed byrepeatedly opening and closing the open/close valve 52 f in a statewhere the open/close valve 52 b is opened and the set pressure of theback pressure valve 59 is set to a low value.

In the circulation process (T3), CO₂ is supplied into the processingcontainer 301 using the fluid supply header 317 (see arrow F4 in FIG.3). The fluid supply header 317 may supply CO₂ at a larger flow ratethan the fluid supply nozzle 341. In the circulation process (T3), sincethe pressure within the processing container 301 is maintained at apressure sufficiently higher than the critical pressure, there is noproblem in drying even when CO₂ in a large flow rate collides with thewafer W surface, or flows in the vicinity of the wafer W surface. Thus,the fluid supply header 317 is used with an emphasis on reducing aprocessing time.

In the pressure raising step, the pressure within the processingcontainer 301 rises to the processing pressure (15 MPa). In the pressurelowering step, the pressure within the processing container 301 islowered from the processing pressure to a predetermined pressure (apressure higher than the critical pressure). In the pressure loweringstep, the processing fluid is supplied into the processing container 301through the fluid supply header 317, and the processing fluid isdischarged from the processing container 301 through the fluid dischargeheader 318. Thus, a laminar flow of the processing fluid that flowssubstantially in parallel to the surface of the wafer W is formed withinthe processing container 301 (see arrow F6 in FIG. 3).

As the circulation process is performed, the replacement of IPA by CO₂within the recess of the pattern of the wafer W is facilitated. As thereplacement of IPA by CO₂ within the recess progresses, the criticalpressure of the mixed fluid gradually decreases as illustrated on theleft side in FIG. 7. Thus, it is possible to gradually lower thepressure within the processing container 301 at the end of each pressurelowering step while satisfying a condition that the pressure is higherthan the critical pressure of the mixed fluid corresponding to the CO₂concentration in the mixed fluid.

<Discharge Process>

When the replacement of IPA by CO₂ within the recess of the pattern iscompleted through the circulation process (T3), a discharge process (T4)is performed. The discharge process (T4) may be performed by closing theopen/close valves 52 a, 52 b, 52 c, 52 d, and 52 e, setting the setpressure of the back pressure valve 59 to a normal pressure, opening theopen/close valves 52 f, 52 g, 52 h, and 52 i, and closing the open/closevalve 52 j. When the pressure within the processing container 301becomes lower than the critical pressure of CO₂ by the discharge process(T4), CO₂ in the supercritical state is vaporized, and is separated fromthe inside of the recess of the pattern. Accordingly, the drying processon one wafer W is completed.

According to the above described exemplary embodiment, in the pressureraising process (T1), CO₂ is supplied into the processing container 301from the fluid supply nozzle 341 below the wafer W. Thus, it is possibleto more reliably prevent a pattern collapse. This point will bedescribed below.

When IPA in a liquid state present on the surface of the wafer W isexposed to the flow of CO₂ in a gas state, the IPA may evaporate, andhere, a pattern collapse may occur. In the pressure raising process(T1), when CO₂ in a gas state is supplied into the processing container301 from the fluid supply header 317 at the side of the wafer W, theflow of CO₂ at a relatively high flow velocity directly collides with apuddle of the IPA, or passes through the vicinity of the puddle of theIPA. Thus, the evaporation of the IPA tends to easily occur.

In contrast, in the present exemplary embodiment, CO₂ ejected from thefluid supply nozzle 341 does not directly flow toward the surface of thewafer W or the space in the vicinity of the surface, but collides withthe lower surface central portion of the holding plate 316, radiallyspreads along the lower surface of the holding plate 316, and then flowsinto the space at the upper surface side of the wafer W. That is, in thepresent exemplary embodiment, there is no direct flow of CO₂ from aprocessing fluid ejecting port toward the surface of the wafer W or thespace in the vicinity of the surface. Thus, it is possible to largelysuppress the IPA from evaporating by the supply of CO₂ in a gas stateinto the processing container 301. Meanwhile, when CO₂ in the gas stateflows into the space at the upper surface side of the wafer W, the flowvelocity of CO₂ is largely reduced as compared to when CO₂ is ejectedfrom the fluid supply nozzle 341. Since the orifice 55 b is present inthe second supply line, the flow velocity of CO₂ ejected from the fluidsupply nozzle 341 is originally small. Accordingly, the evaporation ofIPA is further suppressed.

In the above described exemplary embodiment, the fluid supply nozzle 341is located, for example, just below the central portion of the wafer Waccommodated in the processing container 301, but the present disclosureis not limited thereto. The fluid supply nozzle 341 only has to belocated at a position below the holding plate 316, that is, a positionwhere the fluid supply nozzle 341 is not seen when the holding plate 316on which the wafer W is placed is viewed directly above. That is, theCO₂ gas ejected from the fluid supply nozzle 341 only has to collidewith the lower surface of the holding plate 316 or the back surface (thelower surface) of the wafer W.

Meanwhile, when the position of the fluid supply nozzle 341 largelydeviates from the position just below the central portion of the waferW, the flow of the CO₂ gas within the processing container 301 becomesnon-uniform. Then, the flow of the CO₂ gas may wrap around into thesurface of the wafer W. Thus, it is desirable to dispose the fluidsupply nozzle 341 at a position near the position just below the centralportion of the wafer W. From the viewpoint of preventing or suppressingthe flow of the CO₂ gas from wrapping around into the surface of thewafer W, it is desirable that the fluid supply nozzle 341 ejects CO₂upwards in the vertical direction or substantially directly upwards.

In the above described exemplary embodiment, CO₂ is supplied into theprocessing container 301 only from the fluid supply nozzle 341 over theentire period of the pressure raising process (T1), but the presentdisclosure is not limited thereto. When the pressure of the processingcontainer 301 exceeds the critical pressure (about 7 MPa) of CO₂ as aprocessing fluid, CO₂ may be supplied into the processing container 301from the fluid supply header 317, or may be supplied into the processingcontainer 301 from both the fluid supply header 317 and the fluid supplynozzle 341. Also in these cases, a pattern collapse may be prevented.

However, as in the above described exemplary embodiment, it is desirableto supply CO₂ into the processing container 301 only from the fluidsupply nozzle 341 over the entire period of the pressure raising process(T1). This is because a pattern collapse may be more reliably prevented.In contrast, when CO₂ is supplied into the processing container 301 fromthe fluid supply header 317, the supplied CO₂ may directly collide witha puddle formed of IPA or a mixed fluid containing IPA and CO₂, andagitate the puddle, and thus particles tend to easily occur.

As a result of actual tests, when CO₂ was supplied into the processingcontainer 301 only from the fluid supply nozzle 341 over the entireperiod of the pressure raising process (T1), it was possible to preventa pattern collapse, and the level of occurrence of particles was notproblematic. Meanwhile, when CO₂ was supplied from the fluid supplyheader 317 or from both the fluid supply header 317 and the fluid supplynozzle 341 in the latter half of the pressure raising process (T1)(after the pressure within the processing container 301 exceeded about 7MPa), it was possible to prevent a pattern collapse, but the particlelevel became degraded.

Meanwhile, the use of the fluid supply header 317 may further increase apressure raising speed as compared to the use of the fluid supply nozzle341. Thus, depending on a required particle level, CO₂ may be suppliedinto the processing container 301 using the fluid supply header 317 inthe latter half of the pressure raising process (T1) with an emphasis ona throughput.

For example, a processing fluid used for a drying process may be a fluidother than CO₂ (for example, a fluorine-based fluid). Also, it ispossible to use any fluid that may remove, in a supercritical state, apuddle of a dry-preventing liquid formed on the substrate, as aprocessing fluid. The dry-preventing liquid is also not limited to IPA,but any liquid usable as a dry-preventing liquid may be employed. Asubstrate as a processing target is not limited to the above describedsemiconductor wafer W, but other substrates such as, for example, aglass substrate for an LCD, and a ceramic substrate may be employed.

From the foregoing, it will be appreciated that various embodiments ofthe present disclosure have been described herein for purposes ofillustration, and that various modifications may be made withoutdeparting from the scope and spirit of the present disclosure.Accordingly, the various embodiments disclosed herein are not intendedto be limiting, with the true scope and spirit being indicated by thefollowing claims.

What is claimed is:
 1. A substrate processing apparatus for drying asubstrate having a liquid adhering to a surface thereof, using aprocessing fluid in a supercritical state, the substrate processingapparatus comprising: a processing container; a substrate holderconfigured to horizontally hold the substrate within the processingcontainer in a state in which the surface of the substrate is directedupwards; a first fluid supply unit provided below the substrate held bythe substrate holder, and configured to supply a pressurized processingfluid; a second fluid supply unit provided at a side of the substrateheld by the substrate holder, and configured to supply a pressurizedprocessing fluid; a fluid discharge unit configured to discharge aprocessing fluid from the processing container; and a controllerconfigured to control operations of the first fluid supply unit, thesecond fluid supply unit, and the fluid discharge unit, wherein thecontroller causes the substrate processing apparatus to execute: apressure raising process of supplying the pressurized processing fluidto the processing container so as to raise a pressure within theprocessing container to a processing pressure higher than a criticalpressure of the processing fluid, after the substrate having the liquidadhering to the surface thereof is accommodated in the processingcontainer; and a circulation process of supplying the processing fluidto the processing container and discharging the processing fluid fromthe processing container while keeping a pressure at which at least theprocessing fluid is maintained in the supercritical state, within theprocessing container, and wherein in the pressure raising process, thecontroller causes a supply of the processing fluid from the second fluidsupply unit to be stopped and the processing fluid to be supplied fromthe first fluid supply unit into the processing container until at leastthe pressure within the processing container reaches the criticalpressure of the processing fluid, and in the circulation process, thecontroller causes the processing fluid to be supplied into theprocessing container from the second fluid supply unit.
 2. The substrateprocessing apparatus of claim 1, wherein, in the pressure raisingprocess, the controller causes the supply of the processing fluid fromthe second fluid supply unit to be stopped and the processing fluid tobe supplied from the first fluid supply unit into the processingcontainer until the pressure within the processing container reaches theprocessing pressure via the critical pressure from a point in time whenthe supply of the processing fluid into the processing container starts.3. The substrate processing apparatus of claim 1, wherein, in thepressure raising process, the controller causes the supply of theprocessing fluid from the second fluid supply unit to be stopped and theprocessing fluid to be supplied from the first fluid supply unit intothe processing container until the pressure within the processingcontainer reaches the critical pressure of the processing fluid from apoint in time when a supply of the processing fluid into the processingcontainer starts, and causes the supply of the processing fluid from thefirst fluid supply unit to be stopped and the processing fluid to besupplied from the second fluid supply unit into the processingcontainer, or the processing fluid to be supplied from both the firstand second fluid supply units into the processing container, until thepressure within the processing container reaches the processing pressureafter reaching the critical pressure of the processing fluid.
 4. Thesubstrate processing apparatus of claim 1, wherein the first fluidsupply unit is provided to supply the processing fluid from a positionbelow a central portion of the substrate held by the substrate holder,toward the central portion of the substrate.
 5. The substrate processingapparatus of claim 1, wherein the second fluid supply unit is providedto supply the processing fluid from a side of the substratesubstantially in a horizontal direction.
 6. The substrate processingapparatus of claim 5, wherein the second fluid supply unit is providedto supply the processing fluid in parallel to the substrate from aposition higher than an upper surface of the substrate, at the side ofthe substrate.
 7. A substrate processing method comprising:accommodating a substrate having a pattern formed on a surface thereofand a liquid adhering to the surface, in a processing container; raisinga pressure within the processing container to a processing pressurehigher than a critical pressure of the processing fluid by supplying apressurized processing fluid to the processing container; and performinga circulation process of supplying the pressurized processing fluid tothe processing container and discharging the processing fluid from theprocessing container while keeping a pressure at which at least theprocessing fluid is maintained in a supercritical state, within theprocessing container, wherein, in the raising the pressure, thepressurized processing fluid is supplied from a first fluid supply unitprovided below the substrate until at least the pressure within theprocessing container reaches the critical pressure of the processingfluid, in the performing the circulation process, the pressurizedprocessing fluid is supplied from a second fluid supply unit provided ata side of the substrate, and in the raising the pressure, thepressurized processing fluid is not supplied from the second fluidsupply unit until at least the pressure within the processing containerreaches the critical pressure of the processing fluid.
 8. The substrateprocessing method of claim 7, wherein, in the raising the pressure, theprocessing fluid is supplied into the processing container using thefirst fluid supply unit without using the second fluid supply unit untilthe pressure within the processing container reaches the processingpressure via the critical pressure from a point in time when the supplyof the processing fluid into the processing container starts.
 9. Thesubstrate processing method of claim 8, wherein, in the raising thepressure, the processing fluid is supplied into the processing containerusing the first fluid supply unit without using the second fluid supplyunit until the pressure within the processing container reaches thecritical pressure of the processing fluid from a point in time when asupply of the processing fluid into the processing container starts, andthe processing fluid is supplied into the processing container using thesecond fluid supply unit without using the first fluid supply unit orthe processing fluid is supplied into the processing container usingboth the first and second fluid supply units until the pressure withinthe processing container reaches the processing pressure after reachingthe critical pressure of the processing fluid.
 10. A non-transitorycomputer-readable storage medium storing a computer-executable programthat, when executed, causes a computer to control a substrate processingapparatus to execute the substrate processing method of claim 7.